Algebra

\(\begin{array}{cc} &A + 2 = C + 2\\ \implies & A = C \end{array}\)

 

\(\begin{array}{cc} &B - 2 = D - 2\\ \implies & B = D \end{array}\)

 

\(\begin{array}{cc} &A + 2 = B - 2\\ \implies & B = A + 4 \end{array}\)

 

\(\begin{cases} A = C\\ B = D = A + 4 \end{cases}\)

 

Since A + B + C + D = 36 and with the above system of equation,

\(A + (A + 4) + A + (A + 4) = 36\)

 

Now you can solve for the value of A. If you know the value of A, you know the values of B, C, D. Then you will be able to find the product ABCD.